CIDR in Computer Networking

What is CIDR?

Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and IP routing. It was introduced in 1993 as a replacement for the older system based on classes A, B, and C networks. CIDR is designed to improve the efficiency of IP address allocation and to reduce the size of routing tables.

For more details, visit the Wikipedia article on CIDR.

How CIDR Works

CIDR uses a method called "prefix notation" to define the size of a network. This notation consists of an IP address, followed by a slash ("/") and a number that indicates how many bits of the address are used for the network prefix. For example, 192.168.1.0/24 means the first 24 bits of the IP address are the network part, leaving the remaining bits for host addresses.

Learn more about subnetting and IP addresses.

Example of CIDR Usage

Here is an example of how CIDR can be used:

IP Range: 192.168.0.0 - 192.168.3.255
CIDR Notation: 192.168.0.0/22

Explanation:
- The "/22" means the first 22 bits are used for the network part.
- This gives a total of 2^(32-22) = 1024 IP addresses, ranging from 192.168.0.0 to 192.168.3.255.

Benefits of CIDR

References